Implement RightScale.update_server_array_inputs() method.

Retrieves the next_instance resource collection from RightScale, then
calls the multi_update method to update the next server inputs.
Add 'inputs' as an option for the server_array.Update Actor.

The ServerArray Update Actor now takes both 'inputs' and 'params' as
optional settings that can be used to patch an array.
Bugfix: Use method reference, don't actually execute it
Quiet down the duplicate logging unless we're in dry mode.
Merge pull request #12 from Nextdoor/rightscale_update_actor_issue_7

Issue 7: Allow patching either-or-both server array parameters and inputs.